1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

heatz1express

Petty Officer 2nd Class
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Jun 23, 2004
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115
Looking for guidance.

1984 YAMAHA 115 h.p. 2-stroke with bypassed oil injection running 50:1 pre-mix. I've had it two years and has been minty until recently.
Went from occasional hard start (I tried everything - choke in, choke out, throttle, no throttle, with remote choke and with manual choke, all combinations --- NOTHING and then.. for no explainable reason she fires up on the umpteenth try!!! Once started, ran/runs as it should and can be shut off and re-started no problem. Seems to coincide with being run and then left for a day or two. If I stop for a couple of hours, no problem she fires right up with no choke or throttle needed. At first it did it only once in a while and recently it has been happening more frequently to the point where now it will not start at all! Usually when it happens the engine floods right away, and when it finally starts it smokes quite a bit. Advancing the throttle with no choke does not seem to matter - starts when IT WANTS to start - sometimes with choke on sometimes with choke off, sometimes with or without manual choke set and flicking the remote switch too!

Put new plugs in today and tried. it fired once - then nothing!!! (old plugs were wet and fouled somewhat)

ANY suggestions and I don't mean "Buy a Honda or buy a Merc"! I love my Yamahas - it's just that right now this one is pissing me off!!! I was thinking sticky floats or something. Now beginning to wonder if maybe it is the computer or something electrical.
the stupid thing is, once started, it has always run great - no issues. Although, it does seem to be drinking more fuel than it should be.
A friend suggested that maybe it's the ignition, but wouldn't that sort of problem flair up while running, along with most other possible electrical troubles?

"guidance" would be much appreciated.

Today I checked for spark and discovered that there is none! Atleast not when it won't start. every so often it does fire? so intermittent spark - very weird!
 
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Bamaman1

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May 15, 2011
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1,895
Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

90/10 gasoline wreaks havoc on carb engines. Your motor is the first year of Yamaha's in the U.S.

Sometimes you must take a systematic approach to this problem.

You should start by removing the carbs. and clean them. If you're careful with the gaskets, no carb kit is even needed. Just note how many turns it takes to fully "seat" any adjustment screws. And put them back at the same place when you reassemble it.

I'm not a mechanic, but I can remove, clean and reinstall a pair of these carbs in about 1 hour.

While you're at it, go through your fuel system to make sure there are not clogged filters. And it never hurts to put another fuel pump membrane in--another item affected by 90/10.

Then see how your motor runs.
 

heatz1express

Petty Officer 2nd Class
Joined
Jun 23, 2004
Messages
115
Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

90/10 gasoline wreaks havoc on carb engines. Your motor is the first year of Yamaha's in the U.S.

Sometimes you must take a systematic approach to this problem.

You should start by removing the carbs. and clean them. If you're careful with the gaskets, no carb kit is even needed. Just note how many turns it takes to fully "seat" any adjustment screws. And put them back at the same place when you reassemble it.

I'm not a mechanic, but I can remove, clean and reinstall a pair of these carbs in about 1 hour.

While you're at it, go through your fuel system to make sure there are not clogged filters. And it never hurts to put another fuel pump membrane in--another item affected by 90/10.

Then see how your motor runs.


Thanks for the response. I only ever run high-test gas with yamalube mix and yamaha fuel additive. I thought I was going to have to go in the direction that you suggest and clean the carbs/change the filters. Obviously I will at some point, but having discovered that I have no spark when it won't start - I'm now leaning towards electrical. Maybe the switch box? I don't know!!! I went down to the boat this morning and tried her . She fired but did not start?(Suggesting I had spark for atleast a second! yesterday no spark?

The motor itself looks, inside and out, brand new - awesome condition for the age and the entire leg was replaced with a factory supplied one just a couple of years ago. Yamaha built a hell of a motor in 84, as I'm sure they do now!
 

heatz1express

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Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

O.K. an update. this morning I went down to the boat and gave her a try. nothing! I then proceeded to trim er up to get the leg out of the scum and thought I'd try her again on the way up - she started! Ran, for probably five minutes (I wanted to charge up the battery some) then she quit! (never done that before, once running)

I have checked for loose/damaged wires, I'm getting good fuel flow and I have changed the plugs. Anybody got a theory or possible explanation?
 

99yam40

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Joined
Sep 7, 2008
Messages
8,851
Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

checking peak voltages in and out of CDI should lead you to where the problem is ,
if there is no spark when it does not start.
Specs will be in service manual
 

adam d

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Feb 20, 2014
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Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

hello. i have same set up as you . i am a mechanic on autos and diesels just never been too deep with outboards. my ob was doing exact same thing as yours and i fought it for a while before getting it figured out. the gasket behind the reed housing was sucking air and causing me to loose the suction needed to pull fuel from the carb. bowls. i replaced the gasket and put some boyesen reeds in it while i was there. it fires right up now. before , it would not srart cold no matter what unless you sprayed it with alternate fuel. starts good now ! i have read alot of folks have this problem but did not hear of any fixes. hope this helps . peace out !
 

racerone

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Dec 28, 2013
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36,047
Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

These motors do not like " slow cranking " ----there is a need to inspect starter / wires / battery.---The electronic magneto may not generate spark if flywheel is turning too slow.
 

heatz1express

Petty Officer 2nd Class
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Jun 23, 2004
Messages
115
Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

thanks for the replies guys! solved the problem with mine by replacing cdi. ($600). got a bit more use out of her before the lake froze solid! now I'm chompin' at the bit for SPRING. If she acts up again I'll check the reed/gasket scenario.
 

MikDee

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Jun 6, 2007
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4,745
Re: 1984 115 h.p. 2-stroke --- no start for an hour and then..starts and runs great?

I thought it might be a faulty CDI, not a cheap fix, but extended life & being dependable is worth it!
I had an old 69' 115 Evinrude that used to do the same thing, it was tempermental when cold (it wouldn't start, until it felt like it sometimes :rolleyes: But then ran perfect for the day, hot, or cold!) I used to turn on the ignition, & listen for a faint high pitched whine, if not there, otherwise, you could stand on your head trying to get it started! :confused:

Solved this by getting a later model 135 Johnson to replace it! :)
 
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